Body mass index trend and variability in rheumatoid arthritis

To characterize and compare trends in body mass index (BMI) and variability in BMI between subjects with rheumatoid arthritis (RA) and matched non-RA subjects and to determine predictors of BMI trends and variability within RA subjects.

This retrospective population-based cohort study included 1114 Olmsted County, Minnesota residents, 558 with incident RA (age ≥ 18 years, 1987 ACR criteria met in 1995-2009) and 556 non-RA subjects from the same underlying population with similar age, sex, and index calendar year. All subjects were followed until death, migration, or 12/31/2018. Generalized linear models with smoothing splines and random effects to account for multiple measurements per subject were used to examine trends in BMI measurements over time.

Mean BMI of patients with incident RA (28.8 kg/m²) was not significantly different from that of non-RA subjects (28.9 kg/m²). There was no significant difference in BMI trends over time between RA and non-RA cohorts, or between seropositive for rheumatoid factor (RF) and/or citrullinated antibody (CCP-antibody) and seronegative RA patients, or between male and female subjects. RA subjects were noted to have significantly higher BMI variability following diagnosis compared to non-RA subjects [difference in standard deviation between RA and non-RA subjects prior to index (p = 0.12), 0-5 years after index (p = 0.044), and 5-15 years after index (p = 0.013)].

The BMI trajectory of the RA population is not significantly different compared to that of the non-RA population, but patients with RA demonstrate higher variability in BMI following diagnosis compared to the non-RA population. Key Points • This study uniquely characterizes longitudinal trajectory in BMI measures and their variability in the RA population versus the non-RA population • This study suggests that RA patients have greater BMI variability compared to the non-RA population, which is highly relevant as BMI variability is increasingly understood as a cardiovascular risk factor.